Saratogo's advice is bang on. Integration with your existing chart plotter etc, is a big consideration when deciding which manufacturer to choose from. The most challenging aspect of the install was completing the sea star connections. Careful not to mess up your helm connection, those connector threads are delicate and especially hard to complete in tight spaces. I realized after a while given my situation with extremely tight spaces that it paid to hire an expert to complete the final connections. I installed and ran all the compass, pump and wiring and left the hydraulics to an expert. Also, another bit of advice is to upgrade the pump. That is the weak link in the whole system. If you try to get the smaller less expensive pump to work it may lead to a future failure. Small pumps are OK for single engine applications, but not recommended for twins.
Location of your compass if also very important. Must be as low as possible, dry space (no water), and in the middle of the boat. Also avoid installing it close to any other larger metal objects - location is covered in the install instructions. I also recommend mounting the Pump in a dry space protected from any water or moisture - and they make a bit of noise so if you can find somewhere on the boat where the pump noise could be muffled that will help.
Another tip is I spent the roughly $400 for a remote Fob to steer the system from anywhere on the boat. I just clip the Fob to my bib, and can easily steer the system remotely.
As stated AP is a game changer. Its not a toy, and once installed you will not ever want to go back. It makes my life so much simpler on the water. Like many on this thread I felt I could not justify the expense, and that kept me from making the plunge. If I only knew how good AP made the fishing experience that much more care free.
That said, AP is not for everyone, and I would say that if your not on the water a lot its probably not worth the investment unless you have a bundle of cash sitting around.